Fix 113 hardening issues across entire Go backend

Security:
- Replace all binding: tags with validate: + c.Validate() in admin handlers
- Add rate limiting to auth endpoints (login, register, password reset)
- Add security headers (HSTS, XSS protection, nosniff, frame options)
- Wire Google Pub/Sub token verification into webhook handler
- Replace ParseUnverified with proper OIDC/JWKS key verification
- Verify inner Apple JWS signatures in webhook handler
- Add io.LimitReader (1MB) to all webhook body reads
- Add ownership verification to file deletion
- Move hardcoded admin credentials to env vars
- Add uniqueIndex to User.Email
- Hide ConfirmationCode from JSON serialization
- Mask confirmation codes in admin responses
- Use http.DetectContentType for upload validation
- Fix path traversal in storage service
- Replace os.Getenv with Viper in stripe service
- Sanitize Redis URLs before logging
- Separate DEBUG_FIXED_CODES from DEBUG flag
- Reject weak SECRET_KEY in production
- Add host check on /_next/* proxy routes
- Use explicit localhost CORS origins in debug mode
- Replace err.Error() with generic messages in all admin error responses

Critical fixes:
- Rewrite FCM to HTTP v1 API with OAuth 2.0 service account auth
- Fix user_customuser -> auth_user table names in raw SQL
- Fix dashboard verified query to use UserProfile model
- Add escapeLikeWildcards() to prevent SQL wildcard injection

Bug fixes:
- Add bounds checks for days/expiring_soon query params (1-3650)
- Add receipt_data/transaction_id empty-check to RestoreSubscription
- Change Active bool -> *bool in device handler
- Check all unchecked GORM/FindByIDWithProfile errors
- Add validation for notification hour fields (0-23)
- Add max=10000 validation on task description updates

Transactions & data integrity:
- Wrap registration flow in transaction
- Wrap QuickComplete in transaction
- Move image creation inside completion transaction
- Wrap SetSpecialties in transaction
- Wrap GetOrCreateToken in transaction
- Wrap completion+image deletion in transaction

Performance:
- Batch completion summaries (2 queries vs 2N)
- Reuse single http.Client in IAP validation
- Cache dashboard counts (30s TTL)
- Batch COUNT queries in admin user list
- Add Limit(500) to document queries
- Add reminder_stage+due_date filters to reminder queries
- Parse AllowedTypes once at init
- In-memory user cache in auth middleware (30s TTL)
- Timezone change detection cache
- Optimize P95 with per-endpoint sorted buffers
- Replace crypto/md5 with hash/fnv for ETags

Code quality:
- Add sync.Once to all monitoring Stop()/Close() methods
- Replace 8 fmt.Printf with zerolog in auth service
- Log previously discarded errors
- Standardize delete response shapes
- Route hardcoded English through i18n
- Remove FileURL from DocumentResponse (keep MediaURL only)
- Thread user timezone through kanban board responses
- Initialize empty slices to prevent null JSON
- Extract shared field map for task Update/UpdateTx
- Delete unused SoftDeleteModel, min(), formatCron, legacy handlers

Worker & jobs:
- Wire Asynq email infrastructure into worker
- Register HandleReminderLogCleanup with daily 3AM cron
- Use per-user timezone in HandleSmartReminder
- Replace direct DB queries with repository calls
- Delete legacy reminder handlers (~200 lines)
- Delete unused task type constants

Dependencies:
- Replace archived jung-kurt/gofpdf with go-pdf/fpdf
- Replace unmaintained gomail.v2 with wneessen/go-mail
- Add TODO for Echo jwt v3 transitive dep removal

Test infrastructure:
- Fix MakeRequest/SeedLookupData error handling
- Replace os.Exit(0) with t.Skip() in scope/consistency tests
- Add 11 new FCM v1 tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/repositories/user_repo.go

@@ -34,6 +34,16 @@ func NewUserRepository(db *gorm.DB) *UserRepository {
 	return &UserRepository{db: db}
 }
 
+// Transaction runs fn inside a database transaction. The callback receives a
+// new UserRepository backed by the transaction so all operations within fn
+// share the same transactional connection.
+func (r *UserRepository) Transaction(fn func(txRepo *UserRepository) error) error {
+	return r.db.Transaction(func(tx *gorm.DB) error {
+		txRepo := &UserRepository{db: tx}
+		return fn(txRepo)
+	})
+}
+
 // FindByID finds a user by ID
 func (r *UserRepository) FindByID(id uint) (*models.User, error) {
 	var user models.User
@@ -130,18 +140,28 @@ func (r *UserRepository) ExistsByEmail(email string) (bool, error) {
 
 // --- Auth Token Methods ---
 
-// GetOrCreateToken gets or creates an auth token for a user
+// GetOrCreateToken gets or creates an auth token for a user.
+// Wrapped in a transaction to prevent race conditions where two
+// concurrent requests could create duplicate tokens for the same user.
 func (r *UserRepository) GetOrCreateToken(userID uint) (*models.AuthToken, error) {
 	var token models.AuthToken
-	result := r.db.Where("user_id = ?", userID).First(&token)
 
-	if errors.Is(result.Error, gorm.ErrRecordNotFound) {
-		token = models.AuthToken{UserID: userID}
-		if err := r.db.Create(&token).Error; err != nil {
-			return nil, err
+	err := r.db.Transaction(func(tx *gorm.DB) error {
+		result := tx.Where("user_id = ?", userID).First(&token)
+
+		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
+			token = models.AuthToken{UserID: userID}
+			if err := tx.Create(&token).Error; err != nil {
+				return err
+			}
+		} else if result.Error != nil {
+			return result.Error
 		}
-	} else if result.Error != nil {
-		return nil, result.Error
+
+		return nil
+	})
+	if err != nil {
+		return nil, err
 	}
 
 	return &token, nil
@@ -341,7 +361,7 @@ func (r *UserRepository) SearchUsers(query string, limit, offset int) ([]models.
 	var users []models.User
 	var total int64
 
-	searchQuery := "%" + strings.ToLower(query) + "%"
+	searchQuery := "%" + escapeLikeWildcards(strings.ToLower(query)) + "%"
 
 	baseQuery := r.db.Model(&models.User{}).
 		Where("LOWER(username) LIKE ? OR LOWER(email) LIKE ? OR LOWER(first_name) LIKE ? OR LOWER(last_name) LIKE ?",
@@ -384,7 +404,7 @@ func (r *UserRepository) FindUsersInSharedResidences(userID uint) ([]models.User
 	// 2. Members of residences owned by current user
 	// 3. Members of residences where current user is also a member
 	err := r.db.Raw(`
-		SELECT DISTINCT u.* FROM user_customuser u
+		SELECT DISTINCT u.* FROM auth_user u
 		WHERE u.id != ? AND u.is_active = true AND (
 			-- Users who own residences where current user is a shared user
 			u.id IN (
@@ -417,7 +437,7 @@ func (r *UserRepository) FindUserIfSharedResidence(targetUserID, requestingUserI
 	var user models.User
 
 	err := r.db.Raw(`
-		SELECT u.* FROM user_customuser u
+		SELECT u.* FROM auth_user u
 		WHERE u.id = ? AND u.is_active = true AND (
 			u.id = ? OR
 			-- Target owns a residence where requester is a member
@@ -460,7 +480,7 @@ func (r *UserRepository) FindProfilesInSharedResidences(userID uint) ([]models.U
 
 	err := r.db.Raw(`
 		SELECT p.* FROM user_userprofile p
-		INNER JOIN user_customuser u ON p.user_id = u.id
+		INNER JOIN auth_user u ON p.user_id = u.id
 		WHERE u.is_active = true AND (
 			u.id = ? OR
 			-- Users who own residences where current user is a shared user